1. Field of the Invention
The present invention relates generally to a method of providing a packet data service in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a method of simplifying a protocol structure for packet data service.
2. Description of the Related Art
A mobile communication system is a generic term indicating a system that services voice and data over a wireless network. Mobile communication systems can be categorized according to multiple access methods. A major example is CDMA. The CDMA mobile communication system has evolved from IS-95 that focuses on voice communication to IMT-2000 that additionally provides high rate data transmission. The IMT-2000 system aims at high quality voice transmission, moving picture transmission, Internet browsing, etc.
Various proposals have been made to service voice and data in mobile communication systems. A circuit switched network and a packet switched network are among them. A network structure that allows efficient information transmission should be considered in designing a mobile communication network. This demand will be pressing in the future generation mobile communication system because the increase in the amount of data to be transmitted will be soaring along with the demand for various services.
FIG. 1 illustrates the configuration of a network in a typical CDMA mobile communication system for servicing packet data. Referring to FIG. 1, an MS (Mobile Station) 100 is connected to a UTRAN (Universal mobile telecommunication service Terrestrial Radio Access Network) 102. The UTRAN 102 is connected to a core network including SGSNs (Serving General packet radio service Supporting Nodes) 112a and 112b and GGSNs (Gateway GSNs) 118a and 118b. A connection is made between the UTRAN 102 and the SGSNs 112a and 112b over ATM (Asynchronous Transfer Mode)-layer 2, but no particular protocol is defined for connection between the SGSNs 112a and 112b and the GGSNs 118a and 118b. Layer 3 uses IP (Internet Protocol) commonly for communications between the UTRAN 102 and the SGSNs 112a and 112b and between the SGSNs 112a and 112b and the GGSNs 118a and 118b. The GGSNs 118a and 11 8b are nodes that connect the network to the Internet and manage the IP addresses of GPRS users. An SGSN that a particular MS is connected to is detected according to the IP address of the MS. The SGSNs 112a and 112b are nodes that service the MS 100 and set a PDP (Packet Data Protocol) environment with the GGSNs 118a and 118b and the UTRAN 102. The UTRAN 102 is a logical entity including a plurality of RNCs (Radio Network Controllers) 103a, 103b and 103c for assigning and controlling radio resources.
The MS must establish a connection with the GGSNs 118a and 118b to receive a packet service in the CDMA mobile communication system. To do so, a GTP (GPRS Tunneling Protocol) tunnel must be established between the UTRAN 102 and the GGSNs 118a and 118b. The GTP tunnel is divided into a first GTP path between the UTRAN 102 and the SGSNs 112a and 112b and a second GTP path between the SGSNs 112a and 112b and the GGSNs 118a and 118b. Each GTP path is identified usually by a TEID (Tunnel Endpoint ID). The SGSNs 112a and 112b relay a GTP packet provided through the UTRAN 102 to the GGSNs 118a and 118b according to the TEID.
Though not separately depicted in FIG. 1, a control path and a data path (GTP path) for packet transmission are defined distinctively between the MS 100 and the GGSNs 118a and 118b. Therefore, the core network establishes the data path by processing control messages transmitted in the control path and packet data is transmitted in the data path.
A layered protocol structure for the CDMA mobile communication system is illustrated in FIG. 2. Referring to FIG. 2, the network elements of the core network are based on IP. The IP is different from IP in a higher layer. For example, when the MS 100 conducts IP communications, the IP of the MS 100 is at the same layer as the IP of the GGSNs 118a and 118b. This is also applied to the UTRAN 102 and the SGSNs 112a and 112b. Then the network has two IP layers. In the lower IP layer, PTP (Packet Transfer Protocol) UDP (User Datagram Protocol) connections are established for the first GTP path between the UTRAN 102 and the SGSNs 112a and 112b and for the second GTP path between the SGSNs 112a and 112b and the GGSNs 118a and 118b. Layer 1/layer2 between the UTRAN 102 and the SGSNs 112a and 112b is defined to be ATM/AAL5. No particular connection protocols are defined for layer 1 and layer 2 between the SGSNs 112a and 112b and the GGSNs 118a and 118b. GTP operates over UDP.
For packet communication for the MS 100, a GTP tunnel must be established between the MS 100 and a GGSN (118a or 118b) through PDP session activation. This is called a PDP setup and a control message for GTP tunneling is a GTP-C. While PDP session activation varies according to what entity requests it, the following description is made with the appreciation that the MS 100 requests it.
FIG. 3 illustrates a signal flow for a PDP setup upon request from the MS in a conventional CDMA mobile communication system. Steps 301 to 311 relate to establishing a data path by control messages transmitted in a control path and steps 313 to 319 relate to transmission of packet data in the data path.
Referring to FIG. 3, the MS 100 sets a desired QoS (Quality of Service) and transmits to the SGSN (112a or 112b) an Activate PDP Context Request message containing the QoS in step 301. The SGSN sets TEID 1, a QoS, and an SGSN IP address (SG-IP) and transmits a Radio Access Bearer (RAB) Assignment Request message containing the information for the Activate PDP Context Request message to a serving RNC among the RNCs 103a, 103b and 103c of the UTRAN 102 in step 303. TEID 1 identifies a path in which the SGSN transmits the packet to the RNC. That is, the SGSN attaches TEID 1 to the header of the packet so that the RNC can determine from TEID 1 that the packet is from the SGSN. The SG-IP is the IP address of the SGSN and the QoS is a QoS that the SGSN supports.
The RNC sets TEID 2, a QoS, and an RNC IP address (RN-IP) and transmits an RAB Assignment Response message to the SGSN in step 305. TEID 2 indicates a path in which the RNC transmits a packet to the SGSN. That is, the RNC attaches TEID 2 to the header of the packet so that the SGSN can determine from TEID 2 that the packet data is from the RNC. The RN-IP is the IP address of the RNC and the QoS is a QoS that the RNC supports. Thus a GTP tunnel has been established between the RNC and the SGSN.
Meanwhile, the SGSN generates TEID 3 and a QoS and transmits to the GGSN a Create PDP Context Request message including TEID 3 and the QoS in response for the Activate PDP Context Request message received from the MS 100 in step 307. TEID 3 indicates a path in which the SGSN transmits a packet to the GGSN. That is, the SGSN attaches TEID 3 to the header of the packet so that the GGSN can determine from TEID 3 that the packet is destined for the GGSN. The QoS is a QoS that the SGSN supports for the GGSN.
In step 309, the GGSN sets TEID 4 and a QOS and transmits to the SGSN a Create PDP Context Response message including TEID 4 and the QoS for the Create PDP Context Request message. TEID 4 indicates a path in which the GGSN transmits a packet to the SGSN. That is, the GGSN attaches TEID 4 to the header of the packet so that the SGSN can determine from TEID 4that the packet is destined for the SGSN. The QoS is a QoS that the GGSN supports for the SGSN.
The SGSN transmits an Activate PDP Context Accept message including a QoS available in the current network to the MS 100 in step 311.
After the setup procedure, the SGSN is capable of routing a PDP PDU (Packet Data Unit) between the MS 100 and the GGSN, that is, a communication is possible between the MS 100 and the GGSN.
The MS 100 transmits a PDP PDU to the RNC and the RNC forwards the PDP PDU to the SGSN by TEID 1. The SGSN then routes the PDP PDU to the GGSN by TEID 4.
Meanwhile, the GGSN transmits a PDP PDU to the SGSN by TEID 3 and the SGSN routes the PDP PDU to the RNC by TEID 2. The RNC forwards the PDP PDU to the MS 100. The GTP path for packet transmission is marked with a dotted line in FIG. 4.
Despite the advantage of the convenience of using an IP in the lower network, the following problems are generated in interfacing between the lower protocol layer and the higher protocol layer in the GTP path.
(1) The GTP path from the RNC to the GGSN passes through five protocol layers, which may cause problems with performance;
(2) A QoS profile requested at each GTP path is not ensured in the course of passing through the IP/UDP/GTP protocol layers of the SGSN. That is, congestion at the SGSN may adversely affect each tunnel; and
(3) While ATM protocols are adopted for the whole UTRAN-SGSN-GGSN path, a QoS set in the RNC or GGSN is not ensured during packet routing in the SGSN because the ATM channel terminates at the SGSN and all packet data are handled equally.
The reasons for these problems are that different lower layer protocols may be applied between the RNC and the SGSN and between the SGSN and GGSN and UDPs connected to the RNC and the GGSN are terminated at the SGSN. That is, IP/UDP termination occurs to received data, followed by a change of a GTP TEID and UDP/IP transmission in the SGSN. Logically two-layer switching occurs over UDP/IP.